The invention relates firstly to a flow detector for monitoring an adhesive flow, for example a hotmelt adhesive, in an adhesive applicator.
It is typically found to be problematic for users if it is detected too late that the adhesive flow in an applicator is no longer taking place as desired. There may be various causes for this: for example, a (geared) feed pump may no longer be feeding, an application module may no longer be opening or a directional valve may no longer be functioning correctly.
Such defects are often only detected too late during the process of applying the adhesive. In this case, very many products may possibly already be defective or have been produced without adhesive being applied and represent rejects.
All of the defects mentioned ultimately lead to no adhesive actually flowing any longer to the substrate or product to which it is being applied.
A first approach to eliminating this problem in the prior art is for example to use optical detectors that monitor the movement of the needle of the application module. However, this approach is very complex to implement and substantially concerns just the application module.
It is also known to introduce mechanical sensor devices directly into the adhesive flow. However, mechanical detectors known from other types of fluid (such as water), such as for example impellers, cannot be readily used in the case of adhesives on account of an easily gummed-up mounting.
For the use of adhesives, therefore, very complex flowmeters are known, using the principle of a geared pump (that is to say likewise a mechanical sensor device) to detect flows or quantitatively determine flows. Even when a relatively accurate measurement is possible as a result, such flowmeters are very complex to produce and are also of a very large construction.